It would not surprise me, both sides and their supporters have doctored polls in the past, they exploit the last second voter crowd, who votes for who they think will win rather than who they want, so if they pump up numbers, they think they have to vote for the winner, and yes voters can be this stupid.
Best measure is to watch the candidates themselves, they have the most accurate polling unavailable to the public. If trump starts sweating or hillary doubles down on adds you know one or the other is in trouble. In 12 romney was .5 behind trump in averages, romney was trying really hard, while obama was kicking back.
Obamas personal pollsters crunched the numbers and said you got this in the bag, while romneys said your in big trouble. It holds the same now, if hillary is spending like a drunk sailor on adds in swing states, it likely means the polls are not close to accurate, as no one would waste money if the election was in the bag.